Image sensors and assemblies are well known to those of skill in the art. In these assemblies, an image sensor was located within a housing which supported a window. Radiation passed through the window and struck the image sensor which responded to the radiation. For the image sensor to function properly, the image sensor had to be positionally aligned with the window to within tight positional tolerances.
Beaman et al., U.S. Pat. No. 5,821,532, hereinafter Beaman, which is herein incorporated by reference in its entirety, sets forth a printed circuit board which included a pair of apertures used as alignment features for mounting the image sensor and for mounting the optics which included the window. More particularly, the pair of apertures were used as the mounting reference for the image sensor and then were used as the mounting reference for the optics.
Formation of the assembly using the pair of apertures in the substrate as the alignment features resulted in at least three tolerance accumulations. First, a certain tolerance was associated with the formation, or patterning, of the metallic traces on the printed circuit board (see reference pads 14 and substrate 10 of Beaman FIG. 1). Second, a certain tolerance was associated with the placement of the image sensor on the substrate (see images sensor 32 and substrate 10 of Beaman FIG. 3). Third, a certain tolerance was associated the placement of the optics on the substrate (see Beaman FIG. 4).
After the image sensor assembly was constructed, the lens assembly was placed over the image sensor assembly. The lens assembly was used to focus light on the image sensor. Typically, the lens assembly was attached directly to the substrate after the image sensor assembly was attached to the substrate. After attachment, the lens assembly was adjusted, for example with adjustment screws, to move the lens assembly until the proper focus was attained. This very rough adjustment was labor intensive. Further, a large tolerance was associated with this very rough adjustment.
Disadvantageously, the image sensor assembly had to accommodate the tolerances discussed above. However, as the art moves to smaller, lighter and less expensive devices, the acceptable tolerances for image sensor assemblies diminishes.
In conventional image sensor assemblies, a housing was used to support the window and to hermetically seal the image sensor (see housing 24 and window 25 of Beaman FIG. 4 for example). This housing was typically formed of ceramic which advantageously had excellent resistance to moisture transmission to protect the image sensor from the ambient environment. Further, the ceramic housing was formed with a shelf which held the window and facilitated proper height positioning of the window (see shelf 29 and window 25 of Beaman FIG. 4 for example). However, ceramic is relatively expensive compared to other conventional packaging materials and it is important to form the image sensor assembly at a low cost.
In addition, mounting this housing at the printed circuit board level was inherently labor intensive and made repair or replacement of the image sensor difficult. In particular, removal of the housing exposed the image sensor to the ambient environment. Since the image sensor was sensitive to dust as well as other environmental factors, it was important to make repairs or replacement of the image sensor in a controlled environment such as a clean room. Otherwise, there was a risk of damaging or destroying the image sensor. Since neither of these alternatives are desirable and both are expensive, the art needs an image sensor assembly which is simple to manufacture and service so that costs associated with the image sensor assembly are minimized.